1. Field of the Invention
The present invention generally relates to the conversion of chemical energy to electrical energy and, more particularly, to an electrochemical cell wherein one of the electrodes comprises at least two distinct active formulations, each comprised of a discharge promoter component mixed with at least one electrode active material but in differing formulations. Preferably the electrode having the distinct active formulations is the cathode in a primary electrochemical cell.
2. Prior Art
It is known to provide cathodes formed from layers having differing formulations of electrode active materials. Examples of this include U.S. Pat. No. 4,294,893 to Iemmi et al., which discloses a composite graphite-resin porous electrode structure comprising powdered graphite (and other forms of electrically-conductive carbon, such as acetylene black), resin monomer and a catalyst. The composite structure may be in the form of two layers having different pore sizes. This cell is applicable to use in fuel cells having acid electrolytes wherein the provision of two layers, the pores of one layer being of a different size than the pores of the other layer, allows the catalyst to concentrate in one of the layers or in the zone of contact between them thus achieving a high concentration of catalyst at the site of the electrode reaction, in use.
U.S. Pat. No. 3,565,694 to Chireau is directed to a bipolar electrode comprising two distinct polymeric coatings on a sheet of zinc or other metal. The adhesive inner coating is of isobutylene polymer or copolymer and the outer coating is of ethylene/vinylacetate copolymer. Both coatings include relatively fine particles of carbon black (preferably acetylene black) and relatively coarse particles of graphite or electrolyte-insoluble metal to reduce their resistance and to serve as the electropositive active material.
In contrast to the composite structures and the distinct active coatings described by the prior art, the present invention is directed to increasing the discharge efficiency of an electrochemical cell by using a relatively small amount of a first electrode active formulation comprising a discharge promoter component mixed with at least one electrode active material in contact with a current collector and, a second electrode active formulation contacting the first formulation and having a lesser amount of the discharge promoter component mixed with an increased amount of the at least one electrode active material. In the case of a Li/CF.sub.x cell having at least two distinct active formulations according to the present invention including a carbonaceous diluent as the discharge promoter component, increased delivered capacities of almost 2% to 5% under a heavy drain rate have been realized.